In recent years, optical discs as large capacity record mediums have been developed. For example, CD (Compact Disc) on which music data is pre-recorded, CD-ROM on which computer data is recorded, and DVD (Digital Versatile Disc or Digital Video Disc) with which video information is handled are known. These optical discs are read-only discs. Recently, optical discs such as CD-R (CD-Recordable), CD-RW (CD-Rewritable), DVD-R (DVD-Recordable), DVD+RW (DVD-Rewritable), and DVD-RAM (DVD-Random Access Memory) on which data can be written one time or data can be rewritten are being practically used.
Some contents such as video data and/or audio data recorded on data record mediums such as optical discs should be copyrighted. To copyright such contents, an encryption technology is used. In the encryption technology, besides encrypted data of content, key information composed of key information necessary for decrypting the encrypted data of content and control information for controlling a generation number of which a content can be copied is used. For example, on a read-only optical disc on which encrypted data of content has been recorded, key information has been also recorded thereon. When data is reproduced from such an optical disc using a reproducing apparatus, it reproduces the key information and decrypts the encrypted data of content using the reproduced key information.
When an optical disc is of recordable type (that means a one-time recordable optical disc or a rewritable optical disc; this definition applies to the description that follows), information can be pre-recorded in a pit form. When an optical disc has a portion in which information cannot be rewritten (hereinafter this portion is simply referred to as ROM portion), key information can be recorded to the ROM portion. With the key information, data of content is encrypted. The encrypted data of content can be recorded on the disc. As a real example, the ROM portion may be disposed at the innermost peripheral portion of the disc, a pit portion used for a track servo and formed at predetermined intervals of tracks, or the like.
A technology of which information necessary for generating key information rather than key information itself is recorded to a ROM portion has been disclosed. For example, as a technology for preventing a DVD from being illegally copied has been disclosed. In the technology, media ID data is recorded in a reproduction only region (ROM portion) formed at an innermost peripheral portion of a rewritable DVD. A hash value of the media ID data and MKB (Media Key Block) is encrypted as key data. The key data is recorded on the disc along with encrypted data of content. The media ID data is a value that is unique for each disc. In addition, since the user cannot rewrite the media ID data, even if he or she illegally copies the data portion to another disc, the media ID data of the copied disc is different from the media ID data of the original disc. Thus, it is impossible to decrypt the data portion recorded on the copied disc.
There is a probability of which a hacker illegally obtains key information. In such a case, it is necessary to update the key information to new one. Thus, whenever key information is updated, new key information is added. Consequently, the data amount of the key information in the ROM portion increases. As a result, the data record capacity of the optical disc decreases.
Since rewritable data record mediums—for example optical discs such as above-described CD-R and CD-RW—do not have a ROM portion in which key information can be recorded, the method of which key information is recorded to the ROM portion (namely, user is prohibited from rewriting key information) cannot be used. Thus, before such discs are shipped, the producer side may record key information to individual optical discs. However, in such a method, not only the data record capacity of the optical discs decreases, but the labor performed by the producer side increases. As a result, the production cost of the optical discs rises.
Therefore, an object of the present invention is to provide a record medium, a recording and/or reproducing method for a record medium, and a recording and/or reproducing apparatus for a record medium that allow updated key information not to increase a record data amount thereof.
Another object of the present invention is to provide a record medium, a recording and/or reproducing method for a record medium, and a recording and/or reproducing apparatus for a record medium that allow information such as key information necessary for decrypting data to be recorded even if a disc for use is a rewritable optical disc that does not have a ROM portion.